Of all of the advanced concepts proposed for the large scale production of hydrogen, the process described in U.S. Pat. No. 3,888,750 is probably the most economical. That process is a two-step cycle. At lower temperatures (.ltoreq.100.degree. C.), sulfur dioxide is electrochemically oxidized to produce sulfuric acid on the anode while hydrogen gas is simultaneously generated on the cathode. Sulfuric acid produced in the electrolyzer is then concentrated and catalytically reduced at higher temperatures (&gt;800.degree. C.) into sulfur dioxide and oxygen. Subsequently, the sulfur dioxide is recycled as a reactant in the first step. The reversible voltage for the conventional electrolysis of water is as high as 1.23 V. The use of sulfur dioxide as an anode depolarizer reduces the thermodynamic voltage of an electrolyzer to only 0.17 V (at unit activity for reactants and products). Therefore, the electrolysis process, through the use of electrochemical oxidation of sulfur dioxide (in place of the anodic evolution of oxygen) utilizes theoretically only about 14% of the electric power required in the conventional water electrolysis. Since the catalytic oxidation of sulfur dioxide is highly irreversible on the platinum catalyst currently being used, the activation overpotential on the anode is normally over 0.3 V at a practical current density (say, 200 mA/cm.sup.2). Consequently, one is not able to obtain a voltage efficiency above 50% in an electrolyzer even if the ohmic loss is excluded. Obviously, the anodic overpotential is always one of the major sources of the efficiency loss in the sulfur cycle hydrogen generation process. In order to improve the energy efficiency of a sulfur dioxide depolarized electrolyzer, it is of particular importance to find better electrode materials to use instead of platinum for the catalytic oxidation of sulfur dioxide in an acidic medium.